Cleaning hobs can be a notoriously filthy job , best left for someone else. Hobs are made of vitreous enamel, stainless steel, old ones of cast iron. I have found that as they are made of materials that are not affected by powerful solvents, then it would be permissible to use such chemicals. I tried Nitromors water soluble paint stripper, ( UK) and was amazed at the results,, the burnt-on crust ,gunge, and fat deposits just "jumped-off", after about an hour with the jel that had been applied with a brush. A final rinse and the hob was like new out of the showroom. I must explain that the hob was left by the previous tenents of the house that we rent out.